1. Silicon Drift Detectors - from LOFT to eXTP – M. Feroci, E
Silicon Drift Detectors - from LOFT to eXTP – M. Feroci, E. Del Monte, Y. Evangelista (INAF/IAPS, Rome) on behalf of the INAF/INFN detector group

2. eXTP boundary conditions
The eXTP orbit will have a higher inclination (14 ÷20) than foreseen for LOFT (0÷2.5). A significantly higher radiation damage to the detectors due to deeper passages through the south-atlantic anomaly. Detectors are supposed to be moderately cooled, passively.

3. LOFT vs RXTE orbit
Low altitude orbits allow to benefit of geomagnetic field as a shield to primary cosmic rays.
Low inclination orbit allows to stay away from the South Atlantic Anomaly (lower radiation damage and lower background modulation due to a smaller span of geomagnetic latitudes, lower/no activations, …)
RXTE
Orbital span of geomagnetic latitudes
at different inclinations
LOFT
Trapped proton flux at different inclinations
LOFT
RXTE
Orbit inclination 2.5˚
Orbit inclination 30˚

4. Mitigation strategies
Operations
Reduce as much as possible the orbit inclination (and keep 550 km altitude)
Reduce as much as possible the detector operating temperature
Technology
Improve noise figure (new layout of the charge collecting region)
Adopt new design to confine the charge drift: all events will be single events.
Reduce the pixel volume (lower anode pitch, lower detector thickness)

5. Anode design improvement
LOFT-M3 (2013)
LOFT-2015

6. Large-area SDD – Working principle

7. Large-area SDD – Working principle
Si bulk
X-ray D R I F T
charge
35 mm
read-out anodes
signal
1 mm
Double events (60%)
Single events (40%)

8. Large-area SDD – Confined drift
Si bulk
X-ray D R I F T
charge
35 mm
read-out anodes
signal
1 mm
Single events 100%

9. Total events, with improved anode layout (no confined drift)

10. Single events, with improved anode layout (with confined drift)

11. Single events, with reduced anode pitch (with impoved anode and confined drift)

12. Heritage from LOFT-M3 study

13. Mitigation strategies - conclusions
Assumptions
14 deg inclination and 550 km altitude
-20C as detector operating temperature (see LOFT-M3)
New anode design (already demonstrated)
Confined drift (already produced, tests in 1-2 months)
Results
LAD energy resolution ranges from 140 eV to 340 eV in 5 years
2x reduction in pixel size reduces the same range to 140 eV – 280 eV (but it costs a 2x in number of channels and read-out power)
Reduction in detector thickness offers a further margin (but reduces high-energy response)
Possible annealing procedures: extra-margin for extended operations

15. The PixDD Project

16. Current status: spectral resolution (ref. Bertuccio et al
Current status: spectral resolution (ref. Bertuccio et al. 2015, JINST 10 P01002)
2.3mm
Single (hex) cell: 13 mm2
Anode = 25 pA/cm2
Read-out: SIRIO preamplifier
Energy resolution:
141 eV C
133 eV C
Low-energy threshold: 170 eV

17. Detector Heritage at INFN & FBK
6-inch
Several different geometries and sizes.
Minimum size of individual cell so far: 9 mm2 (squared)

18. Thin-Window technology at FBK
LOFT
LOFT

19. Current status: thin window (Rachevski et al
Current status: thin window (Rachevski et al. 2015, NIM in press; Bufon et al. 2015, submitted to NIM)
6mm
Single (squared) cell: 38 mm2
Anode = 141 pA (370 pA/cm2)
0C
Read-out: SIRIO preamplifier
Energy resolution: 170 eV Mg (1.2 keV)
Count rate: 2100 cts/s (single cell)

21. Joint Working Groups Strong Field Gravity Dense Matter
Strong Magnetism
Observatory Science
LFA/HFA timing & spectroscopy
Polarimetry
LAD
WFM

22. Joint Working Groups Coordinators
A. De Rosa, P. Uttley, ??, ??
J. Poutanen, A. Watts, ??, ??
S. Zane, A. Santangelo, ??, ??
E. Bozzo, J. in ‘t Zand, ??, ??
G. Pareschi (TBC), TBD, ??, ??
A. Santangelo, E. Costa (TBC), ??, ??
S. Zane, M. Feroci, ??, ??
S. Brandt, M. Hernanz, ??, ??

23. White Papers One per Working Group? Yes Aims and structure? LOFT-like
Publication on arXiv or only eXTP Phase A report? No publication
First draft by when? End of the year
Review? End of February
Final version by when? End of March

24. Baseline payload and satellite
11 LFA with 1-mm pixel SDD (TBC)
2 LFA with GPD
40 LAD Modules
3 WFM units with 60deg off-set
Target launch date: 2023 (no later than 2025)
Orbit: 14deg inclination, 550km altitude